At a time when the President is being buffeted by Congress, it is important to note that his defeats are only partial. Mr. Reagan has a way of changing the question being asked on the Hill - and around the country as well. The question now being asked by even old-time spenders is, ''How much can we cut expenditures?'' What a change from the main question in Congress for the last 50 years: ''How much can we spend in order to solve domestic problems?''
Mr. Reagan got almost everything he wanted from Congress in the way of spending reductions in the first two years, though of course he negotiated for more. As a former union leader he knows that he must ask for more to get what he really is after.
The challenge to Mr. Reagan now comes from some of the moderate Republicans as well as the enlarged Democratic ranks, and it focuses on the defense budget where the President already has been defeated on his request for a 10 percent increase in spending.
But what is not given much attention is the fact that Mr. Reagan, elected in part on his promise to build up the military, has again changed the question. His foes, in and out of Congress, no longer ask: ''How much can we cut back on defense spending?'' Instead they ask: ''How much can we cut back on Reagan's defense-spending proposal?''
The fact is that Mr. Reagan is already presiding over a massive defense buildup. At the minimum defense spending will go up 5 per-cent in fiscal 1984. The President's request for a 10 percent increase was, again, mainly a bargaining position. His counsellor, Ed Meese, now says that the President would be willing to accept the difference between 5 and 10; say, 7 1/2 percent. Mr. Reagan may not get that, but he probably will get at least 6 per-cent.